Continuous polymerization of butadiene and styrene



y m} 1951 J. N. STREET ETAL, 2,560,027

CONTINUOUS POLYMERIZATION OF BUTADIENE AND STYRENE Filed Aug. 8, 194? 2 Sheets-Sheet 1 VACUUM PUMP . TO LATEX TO LATEX STORAGE .QINVENTORS dOHN mg-mammwmouo F, ounsnoox BY Q ATII'ORN EYS'.

J y 1951 J. N. STREET ETAL CONTINUOUS POLYMERIZATION OF BUTADIENE AND STYRENE Filed Aug. 8, 194'? 2 Sheets-Sheet 2 Xmb: 2.

mvsu rons JOHN N. STREET AND RAYMOND F. DUNBPOOK ATTORN EYS Patented July 10, 1951 CONTINUOUS .POLYMERIZATION OF BUTADIENE AND STYRENE John N. Street and Raymond F. Dunbrook, Akron; Ohio, assignors' to'The' Firestone -Tire"& Rubber- Company, Akron; Ohio, a corporation of Ohio I Application August 8, 1947,Serial No; 767,504

2 Claims. 1 This invention relates to the manufacture of rubbery polymers of conjugated dienes and to interpolymers thereof with polymerizable vinylcompounds. The invention relates especially to the production of such rubbery polymers by thecontinuous polymerization of the monomers in a single polymerization vessel.

The manufacture of synthetic rubbers in this country has generally been carried out bybatch processes The batch process, as applied to emulsion polymerization, involves charging a polymerization vessel, usually an autoclave designedto operate-under pressure, with anemulsion of the monomers and the necessary catalyst and modifier. At the end of a polymerization cycle,

the charge is completely removed from the auto-- clave and processed thereafter. Then the autoclave-"is're'charged with a fresh batch of reactantsfor "a subsequent polymerization reaction.

Suggestions have been .made to polymerizeemulsionscontinuously by the use of a long-tube as-a polymerization vessel, in order to give suffi I cient opportunity to the monomers and the low" molecular weight intermediates to react. in order? to produce a final product which has essentially a uniform chain length. Others have suggested using several autoclaves in series, through which i the polymerization emulsion is continuously pumped, in order to approximate the reaction time theoretically afforded by the long tube, mentioned above. A disadvantage of these suggestions is that special polymerization reactors are necessary in case of the long tube process,

and a large numberof individual autoclaves must be employed in accordance with the second I suggestion- It is an object of the present invention to provide a simplified process and apparatus for continuously manufacturing synthetic rubber. Another object is to provide a simplified, continuous process and apparatus especially suited tothe use of activated polymerization systems. Other objects will be manifest in the description of the.

invention whichfollows, and in the accompany: ing drawings, .in which:

Fig. .1 is a diagrammatic view of one embodi- 2. clave' l 53, of twenty gall n capacity; suitably jacketed for controlling the temperature of the Contents; and provided with a stirrer n. Four pplytanks are provided as reservoirs or-"fe tanksfo'r" the materials' necessary for the 'man facture of the synthetic rubber. A tank"i2',' su y ofeighteengallbn capacity'jis provided-:for Storing a water solution of the emulsifying agentrz (soap), a tank l3;'suitably of'six gallon capacity, is provided for storing'butadi'neia small tanks M, which may have a capacity'of abo'ut' twoga lons, is" provided for storing "a *solution of' t polymerization catalyst;- and a tank li' suitabl'y. of wo allon c p c y; i provided fcrst rene-on which may bedissolved a modifier); Tanks I'Z l3, l4; and i5 are connected; respectively; to' pipes 16,- I1, l8',"and l8,"which in turn are're spectively' connected" to metering pump'szfl f z 22, and 23, for accuratelyfeeding the polymeriz tion materialsto' autoclave l0, through-a mani fold '24'an'd an autoclave inlet pipe 252' Suitable} valvesas indicated on the drawing,'are"provided-= in each'of the pipes just mentioned. 1 A pressure auge 28- is connected to the manifold 24 to'aid in controlling the desired even, and safe ffiow 'of materials to' the autoclave; A by-pass loading line, indicated generally by numeral' 2'lj com municat'es through suitable valves as indicated;- u to tanks [2,13, and I 5'; and through'a shuteoira' va1ve'28 to autoclave l0';'the loading linez'lfisiof utility in initially loading autoclave l 0' for begin ning a continuous polymerization run orior oth'r special purposes as will be apparent to those-5" skilled in the art ofpolymerization.

The emulsifier tank I2 is provided witna valved-T inlet pipe ZQfthrough which a solution of thef" emulsifying agent is supplied to the tank: Sim larly, the buta'diene tank l3 ands'tyrene tank lfi are respectively provided" with valved inlet pipes1 30 and 3|; and tank I4 is provided-withanfinlet pipe am sealed with a cap. Eac'hpffthe supply: tanks l2, l3, l4, and 15' is provided with-suitablee. sight gauges identified, respectively, as 32:, 33 3432 and 35." Each offthe supply tanks isconnected through suitable valvedpipes to a manifO'1d36,'"-, leading to 'an air-reducing valve-= 371-, which is connected through a pipe 33 to a source of nitro-w gen under pressure (not shown) Each of theipipes connected to manifoldttfidsprovidedwithea valved connecting .pipe, as shown, through which material' may be introduced into the'supply tanks-- individually, or' from. which "pressurer'mayl be-u equalized with atmospheric pressure. It: is also 2 noted that loading line 21 is provided-at the top of vertical extensionthereof :with a pipe-nipples- 39 through which special materials may be charged into the autoclave I8, such as catalyst solution at the beginning of a run.

The means for continuously (or intermittently as desired) withdrawing material from the autoclave will now be described. A drain pipe 48 is connected to the bottom of autoclave I8, and communicates through a valve 4| to a pipe 42. Pipe 42 carries an extension 43 connected to a valve 44, through which samples may be intermittently withdrawn as desired. Pipe 42 communicates through a valve 44 and pipe 45 to a vertical output chamber 46, provided with a sight gauge 41, at the bottom of which is a petcock 48 from which samples may be drawn if desired. The top of chamber 48 is connected through an equalizer pipe 48, and valve 58 to a vertical pipe 5| opening into autoclave I8 and carrying at the top thereof a safety disc 52. Near the bottom of out-put chamber 45, there is attached an exit pipe 53, communicating through valve 54 and pipe 55 to a micro-cam valve 58 for controlling the rate at which latex is withdrawn from the autoclave I8. The valve 55 communicates through a pipe 51, a valve 58 and a view glass 59 to a manifold 68. A suitable by-pass valve SI and a pipe 62 connects pipes 53 and 51, and a sampling valve 63 is provided in this by-pass line.

Means for batch stripping of unreacted monomers from the latex continuously supplied from autoclave I8 will now be described. Manifold 88 is connected through suitable valved pipes 54 and 65 to identical batch strippers 66. 86. Each stripper is provided with a valved drain pipe 61, a valved inlet pipe 58 and a second valved inlet pipe 68 for charging latex stabilizer in the top of each stripper. Each stripper .68 is connected through a valved pipe 18 to a common surge tank H for containing the foam which often accompanies butadiene vapor from a stripper 63 during the early part of a stripping operation. The bottom of the surge tank H is connected through a drain pipe 12 to identical valved return pipes 13, 13 for returning liquid back into strippers 66, 66.

One outlet 14 at the top of surge tank 1I communicates through a valve 15 and pipe 18 to a compressor 11 for compressing butadiene from the surge tank and delivering it through a pipe 18 to a butadiene condenser 19 and from there into a butadiene storage tank 88-. Another outlet 8I at the top of surge tank 1| communicates through a valve 82 and a pipe 83 to an olefin condenser 84 and a storage tank 85 for storing recovered styrene. Tank 85 is in turn connected through a pipe 85 to a vacuum pump 81.

Referring to Fig. 2, there is shown means for continuously stripping unreacted monomers from the polymerized latex, and it is understood that the apparatus shown in Fig. 2 is alternative to the batch stripping apparatus shown in Fig. l. and operatively described in connection with batch strippers 66, 66. Thus, latex from autoclave I8 may be supplied from micro-cam valve 56 into a pipe 88 at the lower lefthand corner of the apparatus shown in Fig. 2. The unstripped latex flows from pipe 88 through a valve 89 into a latex flash tank 98, from which butadiene vapor continually separates through a valved pipe 8i into a latex foam trap 92, any liquid carried into trap 92 being returned to tank 98 through a valved pipe 93. Butadiene leaves trap 92 through a pipe 94 communicating with a manifold 95 and a pipe 96 to a butadiene compressor 81. The compressed butadiene then feeds back into manifold 4 95 and to a butadiene condenser 88, from which the liquid butadiene flows into a butadiene storage tank 99. A back pressure valve I88 is placed in the line of manifold 95. Latex from which most of the butadiene has been removed, as just described, flows from tank 88 through a valved pipe I8I to a latex vacuum flash tank I82, and the remainder of the unreacted butadiene, now under a partial vacuum, as will be understood from the description hereinafter, leaves tank I82 through a valved pipe I83 and enters a latex vacuum foam trap I84, any liquid entering trap I84 being returned to tank I82 through a valved pipe I85. The butadiene separated from liquid in trap I84 is removed therefrom through a valved pipe I86 and connecting pipe I81, from which the butadiene passes through a vacuum pump I88 and a pipe I89 connected to manifold 95, in which the butadiene mixes with butadiene from tank 98 for condensing and storage.

The latex, which has been substantially freed of butadiene, flows from tank I82 through a valved pipe II 8 to a pump I I I and through a Venturi meter I I2 into the upper region of a continuous styrene stripping column I I3. This column is similar to a conventional perforated plate rectifying column, and it is maintained under a vacuum so that styrene and water will vaporize from the latex as the latter trickles down through the column towards the bottom thereof. The completely stripped latex continually flows from the bottom of column II 3 through a valved pipe H4 to latex storage (not shown). Vapor collecting in the upper region of column II3 travels therefrom through a valved pipe II5 into the bottom region of a styrene column foam tank I I6, from which separated liquid flows back into the top of column I I3 through a valved pipe II1. Vapors of styrene and water (containing small amounts of butadiene) flow from the top of foam tank IIS through a valved pipe H8 to a vacuum condenser IIS, and from the discharge pipe I28 into a knock-out drum I2l. Liquid styrene flows from the bottom of drum I2I through a pipe I22 into a styrene decanter I23. Liquid styrene collecting in decanter I23 is continually discharged therefrom through a pipe I24 into a styrene storage tank I25.

Vapor separating from the styrene liquid in drum I2I passes therefrom through a valved pipe I26 to a steam jet I21 for applying suction to knock-out drum I2I; high. pressure steam enters jet I21 through a valved pipe I28. and water vapor containing small amounts of butadiene and styrene pass from jet I21 through a valved pipe I29 into a vacuum condenser I38. Liquid water containing small amounts of styrene flows from condenser I38 through valved pipe I3I back into styrene decanter I23. A valved discharge pipe I32 is attached to the bottom of decanter I23 for removal of separated water.

Uncondensed vapor from condenser I38 passes therefrom through a valved pipe I33 into pipe I81, for recovery of residual butadiene.

The following specific examples are provided to set out the invention more clearly. The examples, in which all parts are listed by weight, are disclosed in connection with the specific apparatus of the invention shown in Fig. 1 of the drawings.

Example 1 The basic polymerization formula, according Steam to which a continuous polymerization run was made, is as follows:

Butadiene was charged into tank [3, styrene containing the modifier, dodecyl mercaptan, was charged into tank l5, a water solution of the catalyst, potassium persulfate, was charged through pipe 31a into tank [4, and a solution of the soap in the remaining water was charged through inlet pipe 29 into tank 12. The autoclave Ii] was then given a half-charge of seven gallons of the various ingredients, making use of by-pass loading line 21, and finally introducing the required amount of catalyst solution through the pipe nipple39, after which it was sealed with a suitable cap. The, contents of the autoclave were then heated by means of the autoclave jacket to 132 F., and stirrer II was started. Metering pumps 20-23 were operated at a rate to deliver a total of about 1.8 gallons of materials per hour into autoclave I0. At the endof each eight-hour cycle, a sample of thelatex was withdrawn through valve 63 and tested and analyzed to provide the data set out in Table I. It is noted that the average conversion was around 50% and the rubber was too soft and sticky to give desired physical properties, but this experiment proved that the apparatus was operative.

TABLE I [Rates in galsjhlz] S-Hr. Emul- Buta- Conversion Cycle sifier dicne Catalyst styrene Total Per Cent 1 0. 88 O. 62 0. 169 0. 185 1. 85 42 2 88 62 163 185 1. 85 63 3 86 60 158 174 1. 79 54 4 .86 .59 .160 .179 1.79 5 89 58 145 166 1. 78 46 6 S8 57 .161 .160 1. 77 44 7 9O 60 160 165 1. 82 48 8 87 59 161 164 1. 78 50 9 89 54 157 .156 1. 74 48 10 I 88 61 .161 176 1. 83 50. 5

Example 2 Another continuous run was made in the manner indicated in Example 1, except that the materials were supplied to the autoclave at a rate of approximately 1.4 gallons per hour. Data obtained upon samples removed at the end of each eight-hour cycle are set out in Table II. It is noted that the average conversion in this example was between 50 and 60%. The polymer was still too soft and sticky to give desired physical properties.

Example 3 Another continuous run was made in the manner indicated in Example 1, except that the input rate of materials to the autoclave was maintained at approximately one gallon per hour. The data on this run, shown in Table III, bring out the fact that after the polymerization had been operating for 15 hours and then through 56 hours, the conversion was substantially in the range of -72 per cent, and the polymer had plasticity comparable to that of commercial copolymers of this type. The physical testing data presented in Table III were obtained in accordance with a standard tire tread stock formula, and indicate that the polymer had fair physical properties.

The figures for extrusion plasticity were ob-- tained in tests with an instrument of the type described in U. S. Patent 2,045,548 to J. H. Dillon et a1. and known as the Firestone Extrusion Plastometer. The plasticity figure represents the time in seconds required to extrude a constant volume of rubber through a given opening by action of a piston activated by a constant pressure of 8%; pounds air, and at a constant temperature of 185 F.

Example 4 Another continuous run was made as in Exr ample 3, except that the liquid level in the autoclave was raised from 14-15 gallons of Example 3 to 18 gallons in this run, and kept at the latter level throughout the run. From the data set out in Table IV, it is noted that the conversion rose to substantially 60% after about 12 hours and then averaged about throughout the rest of the run, ending after 152 hours. After equilibrium was reached in this run, the quality of the polymers was fairly satisfactory and of uniform properties.

TABLE IV Hour Per Cent Extrusion 400% Elonga- Sample Conversion Plasticity Modulus '1 ensue tion 6 too sticky 12 58. 5 14 67. 0 16 72. 5 24 77. 6 32 76. O 40 75. 0 48 72. 0 56 70. 0 64 71. 5 72 66. 5 67. 0 88 67. O 96 68. 5 104 69. O 112 69. 5 70. 0 128 66. 5 136 68. 0 144 68. 0 1.52 67. 0

of more catalyst or by substituting activated formulas for Formula 1, e. g, a redox formula). Also, variations in the temperature of the reaction and rate of flow through the autoclave can be readily adjusted, in accordance with the present disclosure, depending upon the specific polymerization formula employed and other factors herein indicated, as well as upon the desired characteristics of the synthetic rubber to be produced.

Other systems of monomers may be substituted for the butadiene-styrene system specifically disclosed as will be understood by those skilled in polymerizations.

The invention is defined in the appended claims.

What is claimed is:

1. Continuous method of manufacturing synthetic rubber, which includes continuously introducing 75 parts 1,3-butadiene, 25 parts styrene, 180 parts water, emulsifying agent and polymerization catalyst into a single reactor, continuously agitating the ingredients within the reactor, thereby maintaining the ingredients within the reactor in substantially uniformly dispersed condition, maintaining the temperature at 132 F. within the reactor, adjusting-the rate of butadiene by condensation, separately removing the styrene from the dispersion by distillation, and separately condensing the distilled styrene.

2. Continuous method of manufacturing synthetic rubber, which includes continuously introducing parts 1,3-butadiene, 25' parts styrene, parts water, 0.5 part dodecyl mercaptan, 5 parts soap and 0.3 part potassium persulfate into a single reactor, continuously agitating the in-' gredients within the reactor, thereby maintaining the ingredients within the reactor in substantially uniformly dispersed condition, main taining a constant temperature of 132 F. within the reactor, adjusting the rate of introduction of ingredients into the reactor to a constant rate at which a conversion of the monomers butadiene and styrene to copolymerized butadiene and styrene is constant'within the range of 66.5-70%, continuously withdrawing from the reactor dispersion containing polymerized butadiene and styrene, unpolymerized butadiene and unpolymerized styrene, separating the butadiene from the dispersion by evaporation, recovering the separated butadiene by condensation, separately removing the styrene from the dispersion by distillation, and separately condensing the ,distilled styrene.

JOHN N. STREET. RAYMOND F. DUNBROOK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,259,180 Schoenfeld et al. Oct. 14, 1941' 2,363,951 Fikentscher Nov. 28, 1944 2,384,277 Calcott et al Sept. 4, 1945 2,465,363 Faragher et al. Mar. 29, 1949 FOREIGN PATENTS Number Country Date 517,951 Great Britain Feb. 13, 1940 679,897 Germany Aug. 18,1939

OTHER REFERENCES Chem. and Met. (November 1943) Flow Sheet on 5 and 6 pages of Kirkpatrick Article. 

1. CONTINUOUS METHOD OF MANUFACTURING SYNTHETIC RUBBER, WHICH INCLUDES CONTINUOUSLY INTRODUCING 75 PARTS 1,3-BUTADIENE, 25 PARTS STYRENE, 180 PARTS WATER, EMULSIFYING AGENT AND POLYMERIZATION CATALYST INTO A SINGLE REACTOR, CONTINUOUSLY AGITATING THE INGREDIENTS WITHIN THE REACTOR, THEREBY MAINTAINING THE INGREDIENTS WITHIN THE REACTOR IN SUBSTANTIALLY UNIFORMLY DISPERSED CONDITION, MAINTAINING THE TEMPERATURE AT 132* F. WITHIN THE REACTOR, ADJUSTING THE RATE OF INTRODUCTION OF INGREDIENTS INTO THE REACTOR TO A CONSTANT RATE PRODUCING A POLY-MERIZATION CONVERSION IN THE RANGE OF 60-70%, CONTINUOUSLY WITHDRAWING FROM THE REACTOR DISPERSION CONTAINING POLYMERIZED BUTADIENE AND STYRENE, UNPOLYMERIZED BUTADIENE AND UNPOLYMERIZED STYRENE, SEPARATING THE BUTADIENE FROM THE DISPERSION BY EVAPORATION, RECOVERING THE SEPARATED BUTADIENE BY CONDENSATION, SEPARATELY REMOVING THE STYRENE FROM THE DISPERSION BY DISTILLATION, AND SEPARATELY CONDENSING THE DISTILLED STYRENE. 